The present invention relates to a high-speed evaporator defrost system for defrosting refrigeration coils of evaporators in a short period of time without having to increase compressor head pressure.
In refrigeration systems found in the food industry to refrigerate fresh and frozen foods, it is necessary to defrost the refrigeration coils of the evaporators periodically, as the refrigeration systems working below the freezing point of water are gradually covered by a thin layer of frost which reduces the efficiency of evaporators. The evaporators become clogged up by the build up of ice thereon during the refrigeration cycle, whereby the passage of air maintaining the foodstuff refrigerated is obstructed. Exposing foodstuff to temperature increases due to defrost cycles may have adverse effects on their freshness and quality.
One method known in the prior art for defrosting refrigeration coils uses an air defrost method wherein fans blow warm air against the clogged up refrigeration coils while refrigerant supply is momentarily stopped from circulating through the coils. The resulting defrost cycles may last up to about 40 minutes, thereby possibly fouling the foodstuff.
In another known method, gas is taken from the top of the reservoir of refrigerant at a temperature ranging from 80xc2x0 F. to 90xc2x0 F. and is passed through the refrigeration coils, whereby the latent heat of the gas is used to defrost the refrigeration coils. This also results in a fairly lengthy defrost cycle.
U.S. Pat. No. 5,673,567, issued on Oct. 7, 1997 to the present inventor, discloses a system wherein hot gas from the compressor discharge line is fed to the refrigerant coil by a valve circuit and back into the liquid manifold to mix with the refrigerant liquid. This method of defrost usually takes about 12 minutes for defrosting evaporators associated with meat display cases and about 22 minutes for defrosting frozen food enclosures. The compressors are affected by hot gas coming back through the suction header, thereby causing the compressors to overheat. Furthermore, the energy costs may increase with the compressor head pressure increase.
U.S. Pat. No. 6,089,033, published on Jul. 18, 2000 to the present inventor, introduces an evaporator defrost system operating at high speed (e.g. 1 to 2 minutes for refrigerated display cases, 4 to 6 minutes for frozen food enclosures) comprising a defrost conduit circuit connected to the discharge line of the compressors and back to the suction header through an auxiliary reservoir capable of storing the entire refrigerant load of the refrigeration system. The auxiliary reservoir is at low pressure and is automatically flushed into the main reservoir when liquid refrigerant accumulates to a predetermined level. The pressure difference between the low pressure auxiliary reservoir and the typical high pressure of the discharge of the compressor creates a rapid flow of hot gas through the evaporator coils, thereby ensuring a quick defrost of the refrigeration coils. Furthermore, the suction header is fed with low pressure gas, whereby preventing the adverse effects of hot gas and high head pressure on the compressors. Although this patent is fully operational and provides many advantages, the use of two reservoirs as well as an automation system for flushing the auxiliary reservoir proves to be an expensive solution for smallscale systems, such as systems with only one evaporator and compressor.
It is a feature of the present invention to provide an alternative method of defrosting evaporators at high speed for small-scale systems.
It is a further feature of the present invention to use this alternative method simultaneously with refrigeration cycles for medium-scale systems.
It is a still further feature of the present invention to use this alternative method simultaneously with refrigeration cycles for large-scale systems.
According to the above aim of the present invention, and according to a broad aspect thereof, there is provided a high-speed evaporator defrost system comprising a defrost conduit circuit. The defrost conduit circuit has valve means for directing hot high pressure refrigerant gas from a discharge line of at least one compressor and through a refrigeration coil of at least one evaporator of a refrigeration system during a defrost cycle thereof, and back to a suction header of the compressor through a reservoir of the refrigeration system to remove any liquid refrigerant contained in the refrigerant gas prior to returning to the suction header. The reservoir has an internal pressure which is generally at the same pressure as that of a suction header of the compressor thereby creating a pressure differential across the refrigeration coil sufficient to accelerate the hot high pressure refrigerant gas in the discharge line through the refrigeration coil of the evaporator to quickly defrost the refrigeration coil. The reservoir is repressurized after the defrost cycle for using the reservoir in a refrigeration cycle.
According to a further broad aspect of the present invention there is provided a high-speed evaporator defrost system comprising a defrost conduit circuit. The defrost conduit circuit has valve means for directing hot high pressure refrigerant gas from a discharge line of at least one compressor and through a refrigeration coil of at least one evaporator of a refrigeration system during a defrost cycle thereof, and back to a suction header of the compressor through a reservoir of the refrigeration system to remove any liquid refrigerant contained in the refrigerant gas prior to returning to the suction header. The refrigeration system has at least another evaporator in a refrigeration cycle. The reservoir has an internal pressure which is generally at the same pressure as that of a suction header of the compressor thereby creating a pressure differential across the refrigeration coil sufficient to accelerate the hot high pressure refrigerant gas in the discharge line through the refrigeration coil of the evaporator to quickly defrost the refrigeration coil. The reservoir is repressurized after the defrost cycle for using the reservoir in the refrigeration cycle.
According to a still further broad aspect of the present invention there is provided a high-speed evaporator defrost system comprising a defrost conduit circuit. The defrost conduit circuit has valve means for directing hot high pressure refrigerant gas from a discharge line of at least one compressor and through a refrigeration coil of at least one evaporator of a refrigeration system during a defrost cycle thereof, and back to a suction header of the compressor through a principal reservoir of the refrigeration system to remove any liquid refrigerant contained in the refrigerant gas prior to returning to the suction header. The refrigeration system has at least another evaporator in a refrigeration cycle. The principal reservoir has an internal pressure which is generally at the same pressure as that of a suction header of the compressor thereby creating a pressure differential across the refrigeration coil sufficient to accelerate the hot high pressure refrigerant gas in the discharge line through the refrigeration coil of the evaporator to quickly defrost the refrigeration coil. The defrost system has a buffer reservoir for use in the refrigeration cycle for accumulating high pressure refrigerant liquid therein. The principal reservoir is repressurized after the defrost cycle for use in the refrigeration cycle.